Increment Of Kinetic Energy Research Articles

Compaction quality assessment of highway using roller-integrated positive maximum kinetic energy increment detection technique

During conventional highway construction, quality control and acceptance (QC/QA) are based on limited spot tests of material density at random locations which may not comprehensively represent the entire compacted area and are vulnerable to potential biases. Based on roller-integrated positive maximum kinetic energy increment detection technique with real-time kinematic global positioning systems, this research adopted kinetic energy compaction value (KECV) as a real-time monitoring index for the highway compaction quality, and subsequently proposed an KECV-based assessment method to estimate the compaction quality of subgrade and pavement materials. Additionally, a global interpolation method (Green spline) was adopted to obtain estimates for both KECVs and compaction quality at any location on the work area, enabling the analysis of the passing rate of compaction quality for the entire work area. A case study on the Hengyong highway project in China indicates a highly linear correlation between the KECV and the compaction parameters, the compactness of LLL silt, and the relative density of cement-stabilized macadam; therefore, it can serve as a reliable index for monitoring compaction quality. Assessment of compaction quality on the entire work area can be fast and continuously achieved using the proposed method, which can effectively overcome the above limitation of conventional testing, timely feedback compaction information to avoid quality defects, and availably improve the construction quality of highways.

Construction of graphitic carbon nitride nanosheets via an improved solvent exfoliation strategy and interfacial mechanics insight from molecular dynamics simulations

Graphitic carbon nitride (g-C3N4) nanosheets have attracted great attention in the areas of photocatalysis, sensors, energy storages and membrane separations. A three-step exfoliation strategy was designed to use solvent exfoliating g-C3N4 nanosheets from bulk g-C3N4. In the first stage, bulk g-C3N4 was prepared and then exfoliated into g-C3N4 nanosheets by various solvents. In the second stage, molecular dynamics simulations were carried out and the energy barriers for the exfoliations were determined. Various interactions between solvent molecules and exfoliated nanosheet were analyzed. In the third stage, exfoliation was re-carried out according to the result from MD simulation to obtain optimal amount of exfoliated g-C3N4 nanosheets. The experimental result matched with the simulation prediction very well. In combination with simulation and experiment, a successful way to obtain maximum amount of exfoliated g-C3N4 nanosheet was set up. Then a 5.03 mg/mL g-C3N4 suspension was obtained. Meanwhile, a concept of kinetic energy increment was introduced for the first time to explain the exfoliating efficiency of g-C3N4 nanosheets, which greatly reduced the simulation time by 80% compared with the free energies in terms of the potential of mean force.

Resonance-enhanced two-photon ionization of hydrogen atom in intense laser field investigated by Bohmian-mechanics**Project supported by Jilin Province Science and Technology Development Plan Project–Excellent Youth Talents Fund Project, China (Grant No. 20180520174JH) and the National Natural Science Foundation of China (Grant Nos. 11704145 11904050, 11774129, 11747007, and 11534004).

Resonance enhanced two-photon ionization process of hydrogen atom via the resonant laser pulse is studied by Bohmian mechanics (BM) method. By analyzing the trajectories and energies of Bohmian particles (BPs), we find that under the action of high frequency and low intensity multi-circle resonant laser pulses, the ionized BPs first absorb one photon completing the excitation, and then absorb another photon, completing the ionization after staying in the first excited state for a period of time. The analysis of work done by the forces shows that the electric field force and quantum force play a major role in the whole ionization process. At the excitation moment and in the excitation-ionization process, the effect of the quantum force is greater than that of the electric field force. Finally, we discuss the principle of work and energy for BPs, and find that the electric field force and quantum force are non-conservative forces whose work is equal to the increment of mechanical energy of the system. In addition, it is proved that the quantum potential energy actually comes from the kinetic energy of the system and the increment of kinetic energy is equal to that of the kinetic energy of the system.

CFD approach for two-phase CuO nanofluid flow through heat exchangers enhanced by double perforated louvered strip insert

In this study, turbulent flow characteristics of CuO-water nanofluid through heat exchanger pipe enhanced with louvered strips are numerically investigated. Nanoparticles volume fraction (ϕ) varied from 0 to 2%. The louvered strips are mounted in single and double geometries. The slant angle (θ) and the Reynolds number (Re) are within 15° − 25° and between 5000 and 14,000, respectively. (RNG) k − ϵ model is employed based on the finite volume technique. The results illustrated that strong flow disturbance between the wall and the louvered strip is the main reason for turbulent kinetic energy increment. Besides, the nanoparticles improve the thermophysical properties of the working fluid, which results in better heat transfer. The Nu number increases 15.6% by using nanofluid instead of water at Re = 14000. The highest thermal enhancement parameter of 1.99 is obtained at Re = 14000 by using double perforated louvered strip with θ = 25°. The recirculating flow inside the holes can significantly improve the thermal performance.

A theoretical explanation of natural ventilation at roof openings in urban road tunnels

Natural ventilation through openings in the roof of a road tunnel is a green technique that saves energy and greatly improves the air quality inside the tunnel. However, even though multiple tunnels with natural ventilation have been built in China, the theoretical basis for designing and constructing such tunnels is incomplete and there is as yet no uniform and systematic understanding of the natural-ventilation mechanism at the roof openings. Aimed at these problems and based on nearly six years of research and experiments, this paper presents a theoretical explanation of the flow-field characteristics in a road tunnel and the natural ventilation at its roof openings, including (i) the distribution and governing equations for the flow in the tunnel, (ii) the energy governing equation and (iii) the equation governing the natural ventilation at the roof openings. The presented theoretical formulas are consistent with the measured data. The main conclusions are as follows. (1) The airflow in a road tunnel is drag flow resulting from vehicles driving in a restricted space. The flow develops in a bottom-up manner and tends to be stable. The flow velocity is distributed double-logarithmically with height in the tunnel. (2) Moving vehicles are energy sources for the airflow in a road tunnel. Some of the energy transferred from a moving vehicle to the air increases the airflow velocity, while the rest is consumed in turbulence. As the flow develops, the kinetic energy increment decreases gradually and tends to zero, while the energy dissipation decreases gradually and tends to be stable. (3) The air above a road tunnel with roof openings can be sucked into the tunnel by the airflow induced therein by the unidirectional continuous traffic flow. This creates airflow from exterior to interior, but there is no corresponding ‘breathing’ phenomenon. The air inlet velocity at the roof openings differs considerably along the tunnel. It is maximum near the tunnel entrance and decreases gradually along the tunnel, presenting a concave curve.

Theoretical Model of the Axial Residual Velocity of PELE Projectiles Penetrating Thin Metal Targets

With the increase of battlefield target diversity and protection mobility, the disadvantages of traditional armor piercing warheads have gradually become prominent. The conception of the PELE (penetration with enhanced lateral efficiency) projectile was thus proposed. The axial residual velocity of the projectile is a very important indicator of a PELE projectile, which mainly reflects the penetration ability of the PELE projectile. The PELE projectile is a symmetrical structure, so the collision problem can be simplified to plane collision. Furthermore, the two-dimensional plane is axisymmetric, and so it can be further simplified to one-dimensional collision. Based on simplification and assumptions, the mechanism of a PELE projectile penetrating a thin metal target plate was studied using the shock wave theory, and a theoretical model of axial residual velocity has been established in this article. The energy loss during the penetration process was divided into the following parts: the kinetic energy increment of the target plug in the impact region, the internal energy increment of the outer casing and inner core, and the shear energy dissipation of the projectile against the target plate. In addition, the specific methods of determining the energy loss of each part are given in detail. According to the conservation of energy, the approximate calculation formulae of the axial residual velocity of a PELE projectile have been deduced. Finally, the theoretical results were compared with the experimental results under different working conditions, and the results were in good agreement. Therefore, the theoretical model has application value and guiding significance in the field of engineering.

Coherent Clustering Method Based on Weighted Clustering of Multi-Indicator Panel Data

The identification of coherent clusters plays an important role in dynamic equivalence and active split control of power systems. The existing coherent clustering methods often adopt a single indicator, e.g. only based on the power angle curve to identify coherent clusters. In addition, in the coherency identification process, the feature extraction is not sufficient, which may cause the problem of inaccurate grouping. In this paper, a coherent clustering method based on weighted clustering of multi-indicator panel data (WCMPD) is proposed. First, the measurements including power angle increment, terminal voltage, and rotor kinetic energy increment from phasor measurement units (PMU) are selected from panel data to reflect the coherence of the generators. Second, the indicator weights and time weights are calculated based on the cross-sectional and time dimension of the panel data. In order to suppress the shortcomings of the coherent clustering method based on Euclidean distance, three distance functions (“horizontal absolute value,” “rate of change at adjacent time points,” and “fluctuation variation degree”) are defined, and then aggregated. At last, the distance matrices among generators are calculated and the coherent generators can be obtained based on the system cluster method. The simulation results on the EPRI-36 bus system and the North China power grid demonstrate that the proposed method has better clustering results than traditional methods.

Effect of the transient energy input on thermodynamic performance of passive water-in-glass evacuated tube solar water heaters

In this work the effect of the energy input time distribution on thermodynamic performance of a Water-in-glass Evacuated Tube Solar Water Heater (WGET-SWH) is studied, including thermo-hydraulic, first law and second law analysis. Geometrical model was based on a commercial WGET-SWH with nominal capacity of 40 L and 8 evacuated tubes. Simulations were carried out for four different transient energy inputs and 10°, 20°, 27° and 45° collector tilt angles. If tilt angle and total energy input are fixed, the energy input function with larger rates produced larger velocities and temperatures. Nevertheless this temperature increment is negligible for any practical purpose and the increment of kinetic energy is not large enough to affect stratification. Thus cumulated energy rather than energy input rate is significant for systems performance. Several second law indexes are proposed to assess stratification in the storage tank. The internal stratification number was used to compare the performance of WGET-SWH and active energy storage systems, showing that the former can achieve higher levels of stratification at low tilts, even comparable to those obtained in active systems with stratification promoters. The novelty of this work is to assess the influence of the transient energy input on the thermodynamic performance and stratification of a passive solar water heater.

Flow field development and energy evolution in road tunnels with unidirectional uniform traffic

Shallow-buried road tunnel with roof openings is a green energy-saving technology. In this kind of tunnel, natural ventilation and natural smoke extraction can be realized through the roof openings. Now there are four shallow-buried road tunnels in Nanjing. Since operation, this kind of tunnel has been widely praised for the high air quality inside tunnel, but there is yet no regular design method of it. Buried section is the basic unit of this type of tunnel, while fully understanding of the development of flow field and velocity distribution is the foundation of solving the above problem. Based on simplified flow filed in the buried section and Prandtl velocity distribution law, this paper presented the formula of velocity distribution in the buried section. Besides, a 1/10 reduced-scale tunnel experiment platform was built to test the tunnel flow field on 9 kinds of traffic conditions. Energy transfer and dissipation law in the tunnel flow field were explained based on the concept of energy gradient and the formula of velocity distribution. Research showed that the velocity of the flow field increases quickly and then becomes stable with unidirectional uniform traffic. Velocity meets the logarithmic relationship with height. The air velocity in the tunnel varies approximately linearly with the vehicle speed. And the vehicle speed has much more influence on air velocity than the vehicle spacing. The energy transferred to the airflow from vehicles evolved into two parts in the flow field. One part is absorbed by the flow field and converted into the kinetic energy of the flow field itself. The other part is dissipated in turbulence. The kinetic energy increment increases with the height of the tunnel. The dissipation of energy along the tunnel presents an asymmetrical U-shaped distribution. When the flow becomes stable, the dissipation of energy also becomes stable, and the kinetic energy increment approaches zero.

Unwinding of a carbon nanoscroll due to high speed rotation

A carbon nanoscroll (CNS) can be formed easily by rolling a graphene sheet around a carbon nanotube (CNT) [Zhang and Li, 2010, APL, 97, 081909]. When the CNS is driven by the rotary CNT to rotate at a high speed, the attractive interaction within the CNS or between the CNS and CNT is crippled by the centrifugal force on the CNS. The unwinding of CNS is triggered when the kinetic energy increment approaches to the variation of interaction energy of the system during CNS formation. Numerical experiments also indicate that the unwinding of CNS happens earlier when the CNT has a higher rotational speed or the system is at a higher temperature.

Limits on the use of nuclear explosives for asteroid deflection

Recent studies by the US National Research Council identify nuclear explosives as the only current technology able to deflect large asteroids (those exceeding 500m in diameter) or to mitigate impacts of smaller bodies when the warning time is short. Previous work predicts that either a standoff burst or a very low-yield surface burst is easily capable of deflecting a large (1km) asteroid without fragmentation. Alternatively, large near-surface or just sub-surface bursts can sufficiently disrupt and disperse smaller bodies (300m) to ensure that large fractions (in excess of 99.99%) miss the Earth entirely. Even for very short warning times (less than a month), more than 99.5% of a body′s mass can be deflected off of an Earth-bound trajectory. However, successfully deflecting a small body, while avoiding fragmentation, becomes a challenging problem when the required kinetic energy increment is a substantial fraction of the body′s potential. This paper addresses the challenge of preventing the production of substantial low-speed debris while deflecting small bodies with an impulsive method.

The influences of the local impact site and incident energy on the transport behaviors of single copper atom onto Cu (0 0 1) surface

Molecular dynamics (MD) simulation is carried out to study the transport behaviors of a single deposited atom in Cu film homoepitaxy. We consider the normal Cu incident atoms impinging on the Cu (0 0 1) surface at four possible local impact sites (top, bridge, hollow and general). The observed transport behaviors of the deposited atom onto the surface include: direct adsorption (DA), penetration by atomic exchange, and transient penetration (TP), which a deposited atom penetrates the interstitial site and then rapidly migrates to a stable site on the surface. The results show that transport behaviors of the deposited atom are closely related to both the local impact site and the incident energy. The maximum increment of kinetic energy at every impact site approaches to a certain value except for the incident energy below 2.0 eV. Furthermore, as the incident energy is higher than the penetration threshold, TP behavior could be observed again in some energy ranges. This interesting phenomenon, which cannot be explained by the existing theories, is possibly attributed to the dynamical competition between the deposited atom and substrate atoms.

A methodology for analysing lateral coupled behavior of high speed railway vehicles and structures

Continuous increment of the speed of high speed trains entails the increment of kinetic energy of the trains. The main goal of this article is to study the coupled lateral behavior of vehicle-structure systems for high speed trains. Non linear finite element methods are used for structures whereas multibody dynamics methods are employed for vehicles. Special attention must be paid when dealing with contact rolling constraints for coupling bridge decks and train wheels. The dynamic models must include mixed variables (displacements and creepages). Additionally special attention must be paid to the contact algorithms adequate to wheel-rail contact. The coupled vehicle-structure system is studied in a implicit dynamic framework. Due to the presence of very different systems (trains and bridges), different frequencies are involved in the problem leading to stiff systems. Regarding to contact methods, a main branch is studied in normal contact between train wheels and bridge decks: penalty method. According to tangential contact FastSim algorithm solves the tangential contact at each time step solving a differential equation involving relative displacements and creepage variables. Integration for computing the total forces in the contact ellipse domain is performed for each train wheel and each solver iteration. Coupling between trains and bridges requires a special treatment according to the kinetic constraints imposed in the wheel-rail pair and the load transmission. A numerical example is performed.

Energy transfer under impact load studied by molecular dynamics simulation

The process of amorphous silica clusters impact on a crystal silicon substrate is studied by molecular dynamics simulation, focusing on the energy transfer between clusters and the substrate under different impact conditions such as cluster size, impact velocity, and incidence angle. The impact process is divided into cluster deformation stage, cluster resilience stage, and cluster rebound stage according to the courses of energy change during the impact process. The simulation elucidates that the time of impact process of every cluster is only related to cluster size and is independent of impact velocity and incidence angle. The translational energy loss of the cluster and the potential energy increment of the substrate during cluster deformation stage, and the dissipation energy of system are independent of cluster size under the same impact energy and incidence angle. And the translational energy loss of the cluster during cluster rebound stage changes from energy absorption to energy release after the incidence angle becomes more than 60°. The rotational energy of the cluster may be omitted when the incidence angle is less than 15°. The ratios of the rotational energy increment of the cluster, the kinetic energy increment, and the potential energy increment of the substrate to the translational energy loss of the cluster are obviously influenced by impact conditions. And the ratios of the increment of the other categories of energy to the translational energy loss of the cluster are not sensitive to impact conditions.

A study of the numerical heating in electrostatic particle simulations

We study the nonphysical increase of kinetic energy observed in electrostatic particle simulations. Quantitative analysis of the numerical heating is of vital importance in obtaining reliable results in simulation studies. The numerical heating caused by electrostatic fields is discussed with an emphasis on a couple of simulation parameters, such as the ratios of the number of particles N p to that of grid points N x , and Debye length λ D to the grid size Δ x. In this paper a measure called “heating rate” is used for this purpose, which is defined by the relative magnitude of the kinetic energy increment in unit time to the initial energy. The present numerical experiments have revealed that the heating rate may vary in proportion to ( N p N x ) -1 and ( λ D Δx ) -3 . The heating mechanisms are discussed in terms of nonphysical electric fields as observed in the fluctuation spectra of electric fields.